Bill Thompson, Sir William Thompson, and Lord Kelvin all three thank you for this information.
I brought up the Kelvin/thompson question because I did some reading this afternoon. Yesterday I was humiliated by confusing Kelvin and Maxwell.
Today I was at a used book store and found a book called Grear Feuds in Science. It had a chapter on Kelvin and the age of the earth. There I learned about the name change from Thompson the Lord Kelvin, but no one mentioned why it became "kelvin".
Incidently, Kelvin revised his estimate upwards to billions of years, even before the discovery of radioactivity.